Project description:Several ocular diseases such as retinitis pigmentosa are associated with retinal degeneration, a process during which the retina deteriorates due to the gradual death of photoreceptor cells. Although extensive research has been pursued to identify the underlying pathomechanisms, the precise molecular mechanisms that leads to photoreceptor death remains unclear. In this study, we combined the mouse model of light-induced photoreceptor degeneration with single cell RNA sequencing to decipher the transcriptional response of degenerating photoreceptor cells. We additionally performed pseudotime analysis of gene expression changes for both the control and light damaged photoreceptor clusters to analyze the extent of degeneration following a virtual trajectory of severeness. We found a transcriptional heterogeneity of rod photoreceptors in both control and degenerative conditions, and mapped several rod clusters which strongly differ in their transcriptional profile. We defined one of these clusters as the predominant disease-associated rod cluster, containing the most severely damaged rod cells. Pseudotime analysis demonstrated a strong regulation of TGFb signaling and the RISC complex in light damaged photoreceptors suggesting a pivotal role of these mediators in retinal degeneration.
Project description:Purpose: Avian photoreceptors are a diverse class of neurons, comprised of four single cones, the two members of the double cone, and rods. Many distinctive features of photoreceptor subtypes, including spectral tuning, oil droplet size and pigmentation, synaptic targets and spatial patterning, have been well characterized, but the molecular mechanisms underlying these attributes have not been explored. Furthermore, the signaling events and transcriptional regulators driving the differentiation of these diverse photoreceptors are currently unknown. Methods: To identify genes specifically expressed in distinct chicken (Gallus gallus) photoreceptor subtypes, we developed fluorescent reporters that label photoreceptor subpopulations, isolated these subpopulations using fluorescence-activated cell sorting, subjected them to next-generation sequencing, and conducted differential expression analysis. Results: We identified hundreds of differentially expressed genes from photoreceptor subpopulations labeled with rhodopsin, red opsin, green opsin, and violet opsin reporters. These genes are involved in a variety of processes, including phototransduction, transcriptional regulation, cell adhesion, maintenance of intra- and extra-cellular structure, and metabolism. Of particular note are a variety of differentially expressed transcription factors, which may drive and maintain photoreceptor diversity, and cell adhesion molecules that may mediate spatial patterning of photoreceptors and act to establish retinal circuitry. Conclusions: These analyses provide a framework for future studies that will dissect the role of these various factors in the differentiation of avian photoreceptor subtypes. mRNA expression profiling of 5 pairs of photoreceptor subtypes isolated from chicken retinal explants, 3 replicates per sample
Project description:The mammary epithelial tree is a heterogeneous structure that contains two main populations, luminal and basal, with distinct molecular and functional characteristics. The investigation of how this heterogeneity is developed and how it influences breast tumorigenesis has been hampered by the need to perform these studies using animal models due to the lack of relevant, tractable, and fully characterized in vitro models. Comma-1D is an immortalized mouse mammary epithelial cell line that has unique morphogenetic properties particularly its ability to generate cells of luminal and basal lineages. Here, we perform single-cell RNA-seq studies to dissect its heterogeneous nature. Our analysis reveals that Comma-1D cultures consist of two main populations with luminal and basal features and a smaller population with mixed lineage and bipotent characteristics. Additionally, we demonstrate that multiple transcription factors associated with the differentiation of the mammary epithelium in vivo also modulate this process in Comma-1D cultures. Finally, we have used the Comma-1D model to study how the cellular subtype of origin influences the response to cancer-promoting mutations. We found that only cells with luminal molecular features were able to acquire transformed characteristics after an oncogenic HER2 mutant was introduced in their genomes. Overall, the studies present here characterize at a single-cell level the heterogeneity of the Comma-1D cell line and illustrate how the unique properties of Comma-1D cells can be used as an experimental model to study both the differentiation and the transformation processes in vitro.
Project description:Vertebrate vision is mediated by two kinds of photoreceptors, rods and cones, responsible for dim- and bright-light vision, respectively. Gene expression differences among cone subtypes remain poorly understood compared with rods. We generated single-cell transcriptome data using a droplet-based approach to reveal the extent of gene expression diversity among adult zebrafish photoreceptor subtypes. Populations of photoreceptor cells were enriched by using the transgenic zebrafish lines, Tg(rho:EGFP)ja2Tg and Tg(gnat2:EGFP)ja23Tg, which express GFP in rods and all cone subtypes, respectively. By analyzing the single-cell transcriptomes, we found that in addition to the four canonical zebrafish cone types (ultraviolet, blue, green and red), there exist subpopulations of green and red cones in the ventral retina that express red-shifted opsin paralogs (opn1mw4 and opn1lw1). This work lays a foundation for future studies aimed at understanding how molecular differences among cone subtypes affect photoreceptor function.
Project description:The mammary epithelial tree is a heterogeneous structure that contains two main populations, luminal and basal, with distinct molecular and functional characteristics. The investigation of how this heterogeneity is developed and how it influences breast tumorigenesis has been hampered by the need to perform these studies using animal models due to the lack of relevant, tractable, and fully characterized in vitro models. Comma-1D is an immortalized mouse mammary epithelial cell line that has unique morphogenetic properties particularly its ability to generate cells of luminal and basal lineages. Here, we perform single-cell RNA-seq studies to dissect its heterogeneous nature. Our analysis reveals that Comma-1D cultures consist of two main populations with luminal and basal features and a smaller population with mixed lineage and bipotent characteristics. Additionally, we demonstrate that multiple transcription factors associated with the differentiation of the mammary epithelium in vivo also modulate this process in Comma-1D cultures. Finally, we have used the Comma-1D model to study how the cellular subtype of origin influences the response to cancer-promoting mutations. We found that only cells with luminal molecular features were able to acquire transformed characteristics after an oncogenic HER2 mutant was introduced in their genomes. Overall, the studies present here characterize at a single-cell level the heterogeneity of the Comma-1D cell line and illustrate how the unique properties of Comma-1D cells can be used as an experimental model to study both the differentiation and the transformation processes in vitro.
Project description:Human cone photoreceptors represent a rare cell population of the human retina and are largely outnumbered by other retinal cell types. Despite their rarity, cone photoreceptors are critical for optimal daylight vision and their loss has the greatest impact on sight during the progression of retinal dystrophies. This is most applicable to the L/M-opsin cone populations which form the largest proportion of cones in the human retina and are the only cone types present within the fovea, which is responsible for fine detailed vision. Better understanding of the early genesis of these cells within the human developing retina, particularly in relation to the expression of genes that could be involved in regulating early events such as cell fate decision, is required. These molecular determinants could be exploited in vitro to generate more cone photoreceptors within human stem cell-derived retinal differentiation culture systems, suitable for use in cell transpantation therapies or disease modelling purposes. Additionally, the nature of this cell population in terms of their gene expression heterogeneity remains to be defined. State of the art technology has now advanced so that mRNA sequencing can be performed on individual cells, which means the transcriptome of rare cell populations such as cone photoreceptor cells can be interrogated without the need for ample material. Using the AAV2/9 pR2.1:GFP reporter, containing a synthetic promoter region previously characterised to drive expression in cone photoreceptors, we label and isolate human foetal L/M-opsin cone photoreceptors within the 15pcw human retinal retina. Isolated GFP+ cells were separated into individual cells using the Fluidigm C1 microfludics system, before RNA extraction and cDNA library preparation was performed. In total, 74 single cells were captured and processed for RNA sequencing; quality control of the data led to the inclusion of 65 individual cells for the downstream analysis. Principal component analysis revealed a very subtle heterogeneity across the cells, with the highest variability observed according to the first principal component (PC1). Differential gene expression analysis correlated to PC1 led to the identification of 503 significantly differentially expressed genes. Notably, some genes increase in expression across the cells when ordered according to PC1 which have previous associations with photoreceptor maturation, whereas other genes associated with developmental processes became downregulated across the cells. This led to the hypothesis that at this single timepoint in the human foetal retina, developing L/M-opsin cone photoreceptors exist at different stages of maturation. Overlapping genes were identified from comparing RNA seq data from 15pcw single cells and population samples at early and late timepoints of pR2.1:GFP+ cells, which showed the same gene expression trend between experiments. This suggests differences in cell maturation at a single timepoint of development could be representative of their true developmental trajectory. This overlapping gene dataset is also highly useful to define new gene that could be involved in cone photoreceptor development.